Haha, that's cute! Would make a very nice abstract theme, or for a toy-themed world, like the Topaz Passage in Wario Land 4. Heck, with the right assets, you could combine the Toy Block Tower or the Big Board backgrounds with this, and they'd go well perfectly.

I know it's supposed to represent children's toys and everything's supposed to be bright and colorful, but it might still be worth desaturating the foreground block palettes just a little bit. So many bright primary colors in one image is a little hard on the eyes.

I agree the tilesets look decent. I also have to agree thought that the FG bricks indeed seem a bit too bright. Apart from that i can't find any real complaint, so good job Gamma. I especially like the background you made for this.